High molecular weight polymers are widely used for increasing the viscosity of solutions in many fields, such as the oil industry, papermaking industry, water treatment industry, mining industry, cosmetics industry, textile industry and generally in all industrial techniques using thickened solutions. Now, these high molecular weight polymers have the drawback of low resistance to permanent shear compared to the same polymers of smaller size. These shearing stresses acting on high molecular weight polymers lead to cleavage in the macromolecular chains. Thus degraded, the polymer has diminished thickening properties, and the viscosity of the solutions containing it decreases irreversibly. Moreover, these polymers do not allow modulation of the thickening of the composition to which they are added as a function of the temperature of use of the composition.
The applicant's objective was to formulate novel compositions of additives that have better shear resistance compared to the compounds of the prior art, and the rheological behaviour of which can be adapted as a function of the use of the composition to which these additives are added. This objective is achieved by combining associative, thermoreversibly exchangeable additives and an agent for controlling the association and dissociation of these additives. The associated (potentially cross-linked) and exchangeable copolymers offer the advantage of being more resistant to shearing stresses. This characteristic results from the combined use of two particular compounds, a random copolymer bearing diol functions and a compound comprising at least two boronic ester functions.
Polymers in which at least one monomer comprises boronic ester functions are known from document WO2013147795. These polymers are used in the manufacture of electronic equipment, in particular for equipment for which a flexible user interface is required. These polymers are also used as synthesis intermediates. They make it possible to functionalize polymers by coupling with luminescent groups, electron transporting groups, etc. Coupling of these groups is achieved by standard reactions of organic chemistry involving boron atoms, such as for example Suzuki coupling. However, no other use of these polymers, or association with other compounds, is envisaged.
The composition of additives according to the invention offers many advantages. It makes it possible to increase the viscosity of solutions, in particular of hydrophobic solutions comprising them, relative to the compositions of additives of the prior art. The additives of the composition of the invention have inverse behaviour with respect to temperature change compared to the behaviour of the solution and of the rheology additives of the polymer type of the prior art. It also makes it possible to adapt the increase in viscosity and the rheological behaviour of these solutions as a function of their temperature of use.
The applicant also had the objective of formulating novel lubricant compositions which make it possible to reduce the friction between two mechanical components when used cold and when used hot. The compositions used for lubricating mechanical components generally consist of a base oil and additives. The base oil, in particular of petroleum or synthetic origin, exhibits variations in viscosity when the temperature is varied.
In fact, when the temperature of a base oil increases, its viscosity decreases, and when the temperature of the base oil decreases, its viscosity increases. Now, the thickness of the protective film is proportional to the viscosity, and therefore also depends on the temperature. A composition has good lubricating properties if the thickness of the protective film remains approximately constant regardless of the conditions and duration of use of the lubricant.
In an internal-combustion engine, a lubricant composition can be subjected to external or internal temperature changes. The external temperature changes are due to the temperature variations of the ambient air, such as the temperature variations between summer and winter, for example. The internal temperature changes result from operating the engine. The temperature of an engine is lower when starting, in particular in cold weather, than during prolonged use. A lubricant composition that is too viscous at the starting temperature can have an adverse effect on the movement of the moving parts and thus prevent the engine turning quickly enough. A lubricant composition must on the one hand also be sufficiently fluid to be able to reach the bearings quickly and prevent wear of the latter, and on the other hand thick enough to ensure good protection of the engine when it reaches its operating temperature. There is therefore a need for a lubricant composition having good lubrication properties both for the phases of engine starting and for the phases of operation of the engine at its operating temperature.
Addition of additives that improve the viscosity of a lubricant composition is known. The additives that improve viscosity (or viscosity index improvers) currently used are polymers such as the polyalphaolefins, the polymethylmethacrylates, and the copolymers resulting from the polymerization of an ethylene monomer and an alpha-olefin. These polymers are of high molecular weight. In general, the contribution that these polymers make to the control of viscosity is greater the higher their molecular weight.
However, the high molecular weight polymers have the drawback of low resistance to permanent shear compared to polymers of the same nature but of smaller size. Moreover, they thicken the lubricant compositions regardless of the service temperature of the lubricant composition, and in particular at low temperature. The lubricant compositions of the prior art comprising viscosity improvers can exhibit poor lubrication properties during the phases of engine starting.
The lubricant composition according to the invention makes it possible to overcome the aforementioned drawbacks through the combined use of a mixture of two thermoassociative and exchangeable compounds (a copolymer bearing diol functions and a compound comprising boronic ester functions) and of a diol compound in a lubricating base oil. Unexpectedly, the applicant observed that addition of a diol compound made it possible to control the association between a copolymer bearing diol functions and a compound comprising boronic ester functions. At low temperature, the polydiol copolymer has little or no association with the compounds comprising boronic ester functions; the latter reacting with the diol compound added. When the temperature increases, the diol functions of the copolymer react with the boronic ester functions of the compound comprising them by a reaction of transesterification. The polydiol random copolymers and the compounds comprising boronic ester functions then bind together and can undergo exchange. Depending on the functionality of the polydiols and of the compounds comprising boronic ester functions, and depending on the composition of the mixtures, a gel can form in the base oil. When the temperature decreases again, the boronic ester bonds between the polydiol random copolymers and the compounds comprising them are ruptured; if applicable the composition loses its gelled character. The boronic ester functions of the compound comprising them react with the diol compound that is added. It is possible to modulate the kinetics and the temperature window of formation of these associations, and therefore modulate the rheological behaviour of the lubricant composition as a function of the desired use. It is possible, by means of the compositions of the invention, to supply lubricant compositions that have good lubrication properties during the phases of engine starting (cold phase) and good lubrication properties when the engine is at its operating temperature (hot phase).
Thus, a subject of the invention is a composition of additives resulting from mixing at least:                a polydiol random copolymer A1,        a random copolymer A2 comprising at least two boronic ester functions and able to associate with said polydiol random copolymer A1 by at least one transesterification reaction,        an exogenous compound A4 selected from the 1,2-diols and the 1,3-diols.According to an embodiment of the invention, the molar percentage of exogenous compound A4 in the composition of additives, relative to the boronic ester functions of the random copolymer A2 ranges from 0.025 to 5000%, preferably ranges from 0.1% to 1000%, even more preferably from 0.5% to 500%, even more preferably from 1% to 150%.        
According to an embodiment of the invention, the random copolymer A1 results from the copolymerization:                of at least one first monomer M1 of general formula (I):        
in which:                R1 is selected from the group formed by —H, —CH3, and —CH2—CH3;        x is an integer in the range from 1 to 18; preferably from 2 to 18;        y is an integer equal to 0 or 1;        X1 and X2, which can be identical or different, are selected from the group formed by hydrogen, tetrahydropyranyl, methyloxymethyl, tert-butyl, benzyl, trimethylsilyl and t-butyl dimethylsilyl;        or        X1 and X2 form, with the oxygen atoms, a bridge of the following formula        
                                    in which:                            the stars (*) represent the bonds to the oxygen atoms,                R′2 and R″2, identical or different, are selected from the group formed by hydrogen and a C1-C11 alkyl, preferably methyl;                                                or        X1 and X2 form, with the oxygen atoms, a boronic ester of the following formula:        
                                    in which:                            the stars (*) represent the bonds to the oxygen atoms,                R′″2 is selected from the group formed by a C6-C18 aryl, a C7-C18 aralkyl and C2-C18 alkyl, preferably a C6-C18 aryl;                                                with at least one second monomer M2 of general formula (II):        
in which:                R2 is selected from the group formed by —H, —CH3 and —CH2—CH3,        R3 is selected from the group formed by a C6-C18 aryl, a C6-C18 aryl substituted with an R′3 group, —C(O)—O—R′3; —O—R′3, —S—R′3 and —C(O)—N(H)—R′3 with R′3 a C1-C30 alkyl group.According to an embodiment of the invention, the random copolymer A1 results from the copolymerization of at least one monomer M1 with at least two monomers M2 having different R3 groups.        
According to an embodiment of the invention, one of the monomers M2 of the random copolymer A1 has the general formula (II-A):
in which:                R2 is selected from the group formed by —H, —CH3 and —CH2—CH3,        R″3 is a C1-C14 alkyl group,and the other monomer M2 of the random copolymer A1 has the general formula (II-B):        
in which:                R2 is selected from the group formed by —H, —CH3 and —CH2—CH3,        R′″3 is a C15-C30 alkyl group.        
According to an embodiment of the invention, the side chains of the random copolymer A1 have an average length ranging from 8 to 20 carbon atoms, preferably from 9 to 15 carbon atoms. According to an embodiment of the invention, the random copolymer A1 has a molar percentage of monomer M1 of formula (I) in said copolymer ranging from 1 to 30%, preferably from 5 to 25%, more preferably ranging from 9 to 21%.
According to an embodiment of the invention, the random copolymer A2 results from the copolymerization:                of at least one monomer M3 of formula (IV):        
                                    in which:                            t is an integer equal to 0 or 1;                u is an integer equal to 0 or 1;                M and R8 are divalent binding groups, identical or different, selected from the group formed by a C6-C18 aryl, a C7-C24 aralkyl and a C2-C24 alkyl, preferably a C6-C18 aryl,                X is a function selected from the group formed by —O—C(O)—, —C(O)—O—, —C(O)—N(H)—, —N(H)—C(O)—, —S—, —N(H)—, —N(R′4)— and —O— with R′4 a hydrocarbon-containing chain comprising from 1 to 15 carbon atoms;                R9 is selected from the group formed by —H, —CH3 and —CH2—CH3;                R10 and R11, identical or different, are selected from the group formed by hydrogen and a hydrocarbon-containing group having from 1 to 24 carbon atoms, preferably between 4 and 18 carbon atoms, preferably between 6 and 14 carbon atoms;                                                with at least one second monomer M4 of general formula (V):        
                                    in which:                            R12 is selected from the group formed by —H, —CH3 and —CH2—CH3,                R13 is selected from the group formed by a C6-C18 aryl, a C6-C18 aryl substituted with an R′13 group, —C(O)—O—R′13; —O—R′13, —S—R′13 and —C(O)—N(H)—R′13 with R′13 a C1-C25 alkyl group.                                                
According to an embodiment of the invention, the chain formed by the linking together of the R10, M, X and (R8)u groups with u equal to 0 or 1 of the monomer of general formula (IV) of the random copolymer A2 has a total number of carbon atoms ranging from 8 to 38, preferably from 10 to 26. According to an embodiment of the invention, the side chains of the random copolymer A2 have an average length greater than or equal to 8 carbon atoms, preferably ranging from 11 to 16 carbon atoms. According to an embodiment of the invention, the random copolymer A2 has a molar percentage of monomer of formula (IV) in said copolymer ranging from 0.25 to 20%, preferably from 1 to 10%.
According to an embodiment of the invention, the exogenous compound A4 has the general formula (VI):
with:                w3 an integer equal to 0 or 1;        R14 and R15, identical or different, selected from the group formed by hydrogen and a hydrocarbon-containing group having from 1 to 24 carbon atoms.        
According to an embodiment, the substituents R10, R11 and the value of the index (t) of the monomer of formula (IV) of the random copolymer A2 are identical to the substituents R14, R15 and to the value of the index w3 respectively, of the exogenous compound A4 of formula (VI). According to an embodiment of the invention, at least one of the substituents R10, R11 or the value of the index (t) of the monomer of formula (IV) of the random copolymer A2 is different from the substituents R14, R15 or the value of the index w3 respectively, of the exogenous compound A4 of formula (VI). According to an embodiment of the invention, the weight ratio of the polydiol random copolymer A1 to the random copolymer A2 (A1/A2 ratio) ranges from 0.005 to 200, preferably from 0.05 to 20, even more preferably from 0.1 to 10, even more preferably from 0.2 to 5.
The present invention also relates to a lubricant composition resulting from mixing at least:                a lubricating oil; and        a composition of additives defined above.According to an embodiment of the invention, the lubricating oil is selected from the oils of group I, group II, group III, group IV, and group V of the API classification and a mixture thereof. According to an embodiment of the invention, the weight ratio of the random copolymer A1 to the random copolymer A2 (A1/A2 ratio) ranges from 0.001 to 100, preferably from 0.05 to 20, even more preferably from 0.1 to 10, even more preferably from 0.2 to 5. According to an embodiment of the invention, the molar percentage of exogenous compound A4 relative to the boronic ester functions of the random copolymer A2 ranges from 0.05 to 5000%, preferably ranges from 0.1% to 1000%, even more preferably from 0.5% to 500%, even more preferably from 1% to 150%. According to an embodiment of the invention, the lubricant composition of the invention results from additionally mixing a functional additive selected from the group formed by the detergents, antiwear additives, extreme pressure additives, additional antioxidants, viscosity index improving polymers, pour point improvers, antifoaming agents, anticorrosion additives, thickeners, dispersants, friction modifiers and mixtures thereof.        
The present invention also relates to a process for modulating the viscosity of a lubricant composition, the process comprising at least:                supplying a lubricant composition resulting from mixing at least one lubricating oil, at least one polydiol random copolymer A1 and at least one random copolymer A2 comprising at least two boronic ester functions and able to associate with said polydiol random copolymer A1 by at least one transesterification reaction,        adding, to said lubricant composition, at least one exogenous compound A4 selected from the 1,2-diols and the 1,3-diols.The invention also proposes the use of at least one compound selected from the 1,2-diols or the 1,3-diols for modulating the viscosity of a lubricant composition, said lubricant composition resulting from mixing at least one lubricating oil, at least one polydiol random copolymer A1 and at least one random copolymer A2 comprising at least two boronic ester functions and able to associate with said polydiol random copolymer A1 by at least one transesterification reaction.        